Mempool /’mem,pool/ term (noun) a smaller database
that stores pending transactions which every node keeps record of.
[PoV] when a transaction is confirmed by virtue of being included in
a block, it is removed from the mempool.
Off-chain /’off,chain/ term (adjective) to store data
outside of the blockchain.
On-chain /’on,chain/ term (adjective) to store data
on the blockchain.
Sidechain /’side,chain/ concept (noun) a separate
blockchain network that connects to another blockchain - called a
parent blockchain (mainnet) - via a two-way peg.